1. Field of the Invention
The present invention relates to a liquid crystal display device and a method of fabricating a liquid crystal display device, and more particularly, to an in-plane switching mode liquid crystal display device and a method of fabricating an in-plane switching mode liquid crystal display device.
2. Description of the Related Art
Currently, portable electronic devices, such as mobile phones, personal digital assistants (PDAs), and notebook computers, require various types of flat panel display devices. For example, liquid crystal display (LCD) devices, plasma display panel (PDP) devices, field emission display (FED) devices, and vacuum fluorescent display (VFD) devices have all been developed for application as a flat panel display. However, the LCD devices are attractive for their simplified production technology, easy driving means, and high image production quality.
The LCD devices have various display modes according to particular arrangement of liquid crystal molecules. For example, twisted nematic (TN) mode LCD devices are commonly used because of their easy display of black-and-white images, fast response speed, and low driving voltage. During operation of a TN mode LCD device, liquid crystal molecules initially oriented to be parallel with a substrate are oriented nearly perpendicular to the substrate when a voltage is applied thereto. However, when the voltage is applied, the viewing angle is narrowed due to refractive anisotropy of the liquid crystal molecules. Accordingly, various modes of LCD devices having wide viewing angle characteristics have been developed, including in-plane switching (IPS) mode LCD devices.
FIG. 1 is a plan view of an in-plane switching mode LCD device according to the related art, FIG. 2A is a cross sectional view along I-I′ of FIG. 1 according to the related art, and FIG. 2B is a cross sectional view along II-II′ of FIG. 1 according to the related art. In FIG. 1, a pixel of a liquid crystal display panel 1 is defined by gate lines 3a and 3b arranged along a longitudinal direction and data lines 4a and 4b arranged along a direction traverse to the longitudinal direction. Although only the (n,m)th pixel of the IPS liquid crystal display panel is shown, an N-number of gate lines (wherein N>n) and an M-number of data lines (where M>m) are arranged on the liquid crystal display panel 1 to form a plurality of pixels across an entire surface of the liquid crystal display panel 1. A thin film transistor 10 is formed at a region where the gate and data lines 3a and 4a cross, and includes a gate electrode 12 to which a scan signal is supplied from the gate line 3a; a semiconductor layer 13 formed on the gate electrode 12 and is activated as the scan signal is supplied to form a channel layer, and source and drain electrodes 14 and 15.
A common electrode 5 and a pixel electrode 7 are arranged in parallel to the data lines 4a and 4b, and are both disposed within the pixel region. In addition, a common line 20 electrically connected to the common electrode 5 is arranged to be in parallel to the gate lines 3a and 3b on an upper portion of the pixel region. The pixel electrode 7 is electrically connected to a pixel electrode line 22 that includes a portion that overlaps with the gate line 3b and common line 20 of an adjacent (n+1)st pixel. Accordingly, a storage capacitor is formed on the IPS mode LCD device due to the overlap of the pixel electrode line 22, the gate line 3b, and the common line 20.
In the IPS mode LCD device, liquid crystal molecules are initially oriented to be parallel with the common electrode 5 and the pixel electrode 7. However, when the thin film transistor 10 is enabled and the signal is supplied to the pixel electrode 7, a horizontal electric field substantially parallel with the surface of the liquid crystal display panel 1 is generated between the common electrode 5 and the pixel electrode 7. Accordingly, the liquid crystal molecules are rotated along a same plane of the horizontal electric field, thereby preventing gray inversion due to the refractive anisotropy of the liquid crystal molecules.
In FIG. 2A, the common electrode 5 is formed on a first transparent substrate 30, and the pixel electrode 7 is formed on a gate insulating layer 32. Since the common electrode 5 and the pixel electrode 7 are connected to the common line 20 and to the pixel electrode line 22, respectively, it is desirable that the common line 20 and the pixel electrode line 22 are also formed on the first substrate 30 and on the gate insulating layer 32, as shown in FIG. 2B.
Although not shown, a gate electrode 12 of the thin film transistor is formed on the first substrate 30, and the semiconductor layer 13 is formed on the gate insulating layer 32. In addition, the source electrode 14 and the drain electrode 15 are formed on the semiconductor layer 13, and a passivation layer 34 is deposited on an entire surface of the first substrate 30.
In the liquid crystal display panel 1, when the scan signal is supplied to the thin film transistor 10 through the gate line 3a, the thin film transistor 10 is turned ON and an image signal is input to the pixel electrode 7 through the data line 4. Accordingly, the horizontal electric field in parallel to the first substrate 30 is generated between the common electrode 5 and the pixel electrode 7. Thus, the liquid crystal molecules are rotated along a direction of with the horizontal electric field.
A black matrix 42 is formed on a second substrate 40 for preventing light from leaking to the thin film transistor area and between the pixel regions. In addition, a color filter layer 44 is formed on the second substrate for generating colored images, and a liquid crystal material layer 50 is formed between the first substrate 30 and the second substrate 40.
The IPS mode LCD device requires use of a storage capacitor to improve stability of gray level images, and to reduce a flicker phenomenon and reduce generation of residual images. In order to form the storage capacitor, the LCD devices commonly include storage-on-gate (SOG) structures and storage-on-common (SOC) structures. In the SOG structures, a pixel electrode line is arranged to overlap a gate line to form a storage capacitor. In the SOC structures, a common line is formed within a pixel region and a pixel electrode line is arranged to overlap the common line to form a storage capacitor.
However, LCD devices using the SOG and SOC structures have the following problems. First, in the SOG structures, since the gate line is formed having a set width, overlap of the gate line and the pixel electrode line is limited. Accordingly, sufficient amounts of storage capacitance cannot be achieved. Second, in the SOC structures, even though overlap of the common line and the pixel electrode line can be controlled to provide sufficient amounts of storage capacitance by enlarging the widths of the common and pixel electrode lines, the aperture ratio of the LCD device is lowered due to the enlarged widths of the common and pixel electrode lines.
To resolve these problems, hybrid-type LCD devices have been developed that combine advantages of the SOG and SOC structures to ensure sufficient amounts of the storage capacitance by overlapping the pixel electrode line with the common and gate lines. The IPS mode LCD devices shown in FIGS. 1, 2A, and 2B include the hydrid-type LCD devices. For example, in FIG. 2B, the common line 20 is arranged near the gate line 3b of the adjacent (n+1)st pixel, and the pixel electrode line 22 overlaps with portions of the gate line 3b and the common line 20 of the (n+1)st pixel. However, first and second widths t1 and t2 (in FIG. 1) of the common line 20 and the pixel electrode line 22 must both be formed having larger widths to ensure sufficient amounts of storage capacitance, thereby limiting the aperture ratio.